Well, it's sad but it was already done. So, I will share with you guys a good tool to download mangas to your comp and you can read them even if the provider dies.
Google a tool named domdomsoft manga downloader . It contains all the collection of various online manga provider sites such as: onemanga(nomore); mangafox, mangareader, tenmanga etc... You dont even have to visit their page to navigate or read or anything like that. Just open the tool, search the mangas you want, and download them to your comp. Ofcuz if you dont have an idea of what to read, you can visit their forums for some tittle then search with the engine and get what you want. 100% Free too.